A gritty war video apparently showing U.S. troops firing on a group of civilians in Iraq has been leaked on the Internet.

The disturbing footage, posted on a Web site called Wikileaks.org, shows graphic gun camera images of a U.S. helicopter attack in the New Baghdad District of eastern Baghdad, July 12, 2007.

In the video, a U.S. Army Apache helicopter pilot repeatedly requests permission to fire on a group of men he believes to be insurgents.

The troops then opened fire with machine guns as the men on the ground - some of them unarmed - tried to flee.

More than a dozen people were killed in the attack, including a Reuters photographer. Two children were also wounded.

The incident had been reported before, but the video had not been released previously. Security analysts say the action by the troops is not uncommon in dangerous urban warfare.

"The thing about the Iraq war, and certainly by 2007 this was true, is that you had friends and enemies everywhere on the battlefield," explained Michael O'Hanlon, a defense policy expert at the Brookings Institution.

"And so that, for the most part, meant that if you got into trouble as a Westerner, you had potential help not too far away," he continued. "That was reassuring, but it also meant that if you were unidentified, you had potential friendly fire not too far away at a moment's notice."

After investigating the incident, the U.S. military concluded the troops acted appropriately under the circumstances.